Kids Research Express

. The simplest invertebrates (animals without backbones) do not have specialized digestive organs. Single-celled organisms, such as amoebas , rely on intracellular digestion (digestion within the cell). Some many-celled organisms, such as the sponge, also use intracellular digestion. The sponge obtains the tiny organic particles that make up its diet from water passing through its body. Water enters through the sponge’s pores and leaves through an opening called the osculum. As water flows through the interior canals of the sponge, specialized cells that line these canals, called collar cells, catch and engulf organic matter. Inside the collar cells, sacs called vacuoles form around the food and enzymes digest it. The digested food then passes to other cells in the sponge’s body. Intracellular digestion meets the needs of simple animals, but more complex organisms require systems that are more specialized. Animals such as jellyfish and nonparasitic flatworms combine the intracellular...

The simplest invertebrates (animals without backbones) do not have specialized digestive organs. Single-celled organisms, such as amoebas , rely on intracellular digestion (digestion within the cell). Some many-celled organisms, such as the sponge, also use intracellular digestion. The sponge obtains the tiny organic particles that make up its diet from water passing through its body. Water enters through the sponge’s pores and leaves through an opening called the osculum. As water flows through the interior canals of the sponge, specialized cells that line these canals, called collar cells, catch and engulf organic matter. Inside the collar cells, sacs called vacuoles form around the food and enzymes digest it. The digested food then passes to other cells in the sponge’s body. Intracellular digestion meets the needs of simple animals, but more complex organisms require systems that are more specialized. Animals such as jellyfish and nonparasitic flatworms combine the intracellular pro...